Pauses and hesitations in spontaneous speech are assumed to result from problems in various aspects of sentence planning. A causal role for difficulties with lexical access is suggested by theoretical accounts of speech production [Levelt, Speaking (1989)] and empirical studies showing that pauses are more likely before rare than common words in spontaneous speech [Maclay and Osgood (1959)]. In the present study, word frequency was manipulated in a picture-naming task in which speakers produced the names of ten high- and ten low-frequency pairs of standardized line drawings within a standard sentence frame (e.g., There is a snail to the left of the harp.). The mean frequency of occurrence for high- and low-frequency items was 171.5 (range: 50--591) and 3.5 (range: 1--8) per million, respectively [H. Kucera and W. N. Francis, A Computational Analysis of Present-day English (1967)]. Analyses indicate that low-frequency pairs resulted in: (1) more pauses and word substitutions and (2) longer latencies to begin speaking.